Linkage, Recombination and Eukaryotic Gene Mapping

Question 1

What are the key concepts of linkage, recombination and crossing over?

Answer 1

-genes that are on the same chromosome travel through meiosis together
-alleles of chromosomally linked genes can be recombined by crossing-over

Question 2

What is the concept of linked genes?

Answer 2

-some genes do not segregate randomly
-morgan: genes are linked if present on the same chromosome
-the divergence from linkage is called recombination
-sturtevant: the frequency pf recombination reflects distance between genes

Question 3

How does independent assortment occur with recombination in meiosis?

Answer 3

-rare but stills happens
-Metaphase 1: maternally inherited chromosomes
paternally inherited chromosomes
-dihybrid generates 4 equal gametes
-anaphase 1: the chromosomes disjoin and their alleles segregate from each other
-telophase 1: combinations of chromosomes and alleles are separated into different cells
-telophase II: each combination of alleles is recovered in one-fourth of the products of meiosis

Question 4

Does the inheritance pattern of one trait affect the inheritance pattern of another trait?

Answer 4

-no ratio (9:3:3:1)
-self fertilization of the F1 heterozygotes yields four phenotypes in a 9:3:3:1 ratio

Question 5

What are possible explanations for the Bateson and Punnett observation?

Answer 5

-the R and L genes are linked on the same unit of heredity (chromosome)
-for this reason the RL and rl alleles segregate as linked genes
-there is some infrequent exchange between the units that harbor RL and rl
-call this recombination where crossing over occurs
-can result in recombinant chromosomes
-alleles are swapped, not kicked out which is proportional to abundance

Question 6

How do you calculate the frequency of recombination?

Answer 6

-scoring the Rl and rL phenotypes
-will be different pairs of genes
-if there is a major number it says that there is a strong preference for this allele
-4 different genotypes so you except 4 different groups

Question 7

What is homologous recombination?

Answer 7

-occurs during prophase I of meiosis
-a tetrad or bivalent means 4 homologous chromatids is formed
-a chiasma (point of contact) the site where recombination occurs
-alleles are traded at chiasma

Question 8

What occurs when there is no crossing over?

Answer 8

-homologous chromosomes pair in prophase I
-no recombination therefore each gamete recieves a nonrecombinant chromosome with an original combination of alleles

Question 9

What occurs when there is crossing over?

Answer 9

-takes place in prophase I
-swaps spots in the same allele
-have not created a new combination
-half of the resulting gametes will have unchanged chromosome (nonrecombinant)
-half will have recombinant chromosomes
-the farther apart A and B are the more likely recombination will occur

Question 10

What make crossing over likely to occur?

Answer 10

Closer genes are to each other on the chromosome, the likelier they are to crossover together, which decreases the likelihood of a recombinant gene
-when genes are more distant from one chromosome, the likelier they are to crossover independent from another generating recombinant gametes

Question 11

How do you calculate chromosome mapping?

Answer 11

-number of recombinants (identify in test cross)/ total number of offspring x 100= map unit

Question 12

What are the three possible scenarios for a dihybrid cross?

Answer 12

-genes A and B are independently assorting (9:3:3:1)
-genes A and B are tightly linked so that crossing over does not happen (3:1)
-genes A and B are linked and crossing over o curs (monohybrid cross) (3:1)

Question 13

What is recombination frequency and Genetic Map distance?

Answer 13

-plateau of 50% combination
-dihybrid females
-when two genes are not liked you get 4 equal gametes

Question 14

What is the geneotype of the Hihybrid Parent?

Answer 14

-A L/a l cis trans configuration or
- a L/A l trans configuration
-the parentals tell you what alleles are together on the dihybrid parent
-dihybrid x al/al
-top chromosome come from the dihbybrid and are in the parental configuration
-the bottom chromsome comes from the homozygous parent

Question 15

What is the genetic distance between Genes A and L?

Answer 15

-the two smaller classes are the recombinants they will tell you the distance between the two genes

Question 16

How do you calculate the genetic distance between genes A and L?

Answer 16

-number of recombinants / total number of offspring x 100 - map units
BEFORE CROSS:
All organsims have the same map units distance apart
Generate both new recombinants
AFTER CROSS: two alleles are at the bottom chromosomes
-recombinant chromatids are produces 10.8 & of the time
The frequency of recombinant gametes is 10.8%
-after meiosis the parental gametes have a frequency of 100-10.8 = 89.2 %
-have a dihybrid indiviudally assorted

Question 17

What are linkage and pedigrees?

Answer 17

Use this information to generate elaborate genetic maps and to track the inheritance of certain genes and genetic disorders of other races
Parental gametes is more likely to get in contact with another and have linkage

Question 18

How does genetic linkage between blood types and NPSI mutation occur?

Answer 18

-mutation causing the gene for the B blood group phenotype
-recombination frequency between B and NPS1 is estimated and used for mapping of N gene

Question 19

How do you calculate the recombination frequency?

Answer 19

-divide the number of recombinant people by total

Question 20

What are the key points fo pedigree analysis?

Answer 20

-provides estimates of recombination frequencies to map genes on human chromosomes
-maps are more elaborate and better to use
-can have a limited success inc complex genetic traits

Question 21

What pedigrees and Medical Genetics?

Answer 21

-genetic disorders and their analysis
-pedigrees and medical research
-contemporary genomics linkage and pedigree analyses